Decomposable resins and decomposable resin compositions means resins decomposable in response to an external factor, for example, a thermal factor, a mechanical factor, a photochemical factor, a radiation-chemical factor or a factor with a chemical agent and are well known. Change in the form (liquefaction or vaporization) or change in the nature or property, for example, molecular weight, hardness, viscoelasticity, glass transition point (Tg), solubility or adhesiveness of the resin or resin composition before and after the decomposition, which is caused by the decomposition of resin, is utilized in various fields.
Examples of the decomposable resin and decomposable resin composition include a biodegradable plastic (for example, polylactic acid) for decreasing environmental impact of plastic material and a slow releasing material which can gradually release a component, for example, medical agent or fragrance in the field of healthcare, cosmetic or life science. However, they gradually decompose by oxygen, light or enzyme in a natural environment, within the living body, in the soil or the like and thus they do not stably maintain their initial states and can not induce at once a large change in the nature upon the external stimulation.
Resins which are decomposed by light or heat for improvement in the recycling efficiency or simplification of the disposal and adhesives which decrease the adhesiveness thereof are also developed. Further, it is known that ceramic or carbon fiber is mixed with a decomposable resin and then the decomposable resin is removed, for example, by calcination to form a porous material. However, in these cases, the materials are altogether treated or processed and it is not intended to form the desired pattern only in the desired portion. Also, large energy is required for the decomposition treatment.
With respect to the application to image formation, for instance, it is known that both preservation stability and image fixability of toner are achieved by utilizing change in the nature due to heat at the heat-fixing of the toner containing a heat-decomposable resin. However, the resin per se does not have sufficient response to the pattern-wise stimulation.
As for pattern-forming materials, on the other hand, for example, a so-called chemically-amplified resist is well known as a photoresist. Specifically, a composition containing an acid generator and an acid-decomposable resin is pattern-wise exposed followed by heat treatment, if desired, to decompose pattern-wise the resin and the pattern is formed with development processing. Although the composition satisfies both the preservation stability and the pattern-forming property at a practical level, the development process in which the processing conditions are fully controlled is indispensable for the formation of pattern. Further, the pattern-formation in a thick layer having, for example, several tens of micrometers or more is difficult, though it is possible to apply to a thin layer.
A method of forming an image utilizing a step of removing (ablation) a part of thin layer by imagewise irradiation of laser beam is also known (JP-A-10-119436 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)). However, the compounds recited as the heat-decomposable resin are only conventional general-purpose resins, for example, polyesters, polycarbonates or polyurethanes, and the thickness of the layer is only around 1 to 2 μm. It is also known to use a compound defined its heat decomposability (JP-A-10-244751 (corresponding to US 2002/0098439 A1)). However, the thickness of the layer described therein is also only around 1 to 2 μm.
As a mask material for paste printing to a printed circuit board or the like, a mask for forming a pattern having approximately 100 to 200 μm utilizing a photo-decomposable resin sheet and a production method of the mask are described (JP-A-8-258442). However, a specific compound does not disclosed in the patent. Also, the controlled development processing is indispensable in order to form the pattern while regulating the degree of exposure and development.
On the other hand, in order to form a pattern in a thick layer by a simple process, for example, pattern-formation by laser processing is known, in which the base material per se is removed, deformed or discolored by imagewise irradiation of laser beam. For instance, a method of recording information, for example, a lot number on a product (for example, video tape or home electric appliances) composed of a variety of base materials is utilized as a laser maker. In such cases, conventional resins are used as they are as the base material.
In the pattern-formation by laser processing, it is desired that a laser engraving portion (concave portion) be rapidly formed. For this purpose, a high-sensitive laser-decomposable pattern-forming material is needed.
In particular, in case of a flexographic printing plate precursor of a direct drawing type by laser (so-called flexographic printing plate precursor for laser engraving), since ease of engraving by laser beam (engraving sensitivity) dominates plate-making speed, a flexographic printing plate precursor for laser engraving using a high-sensitive laser-decomposable resin composition has been required.
On the other hand, as an example of composition containing a base generator, positive type photoresists containing a base generator are known (JP-A-2000-10270 and JP-A-2004-250650). In these examples, however, it is intended not to cause depolymerization of a polymer main chain but to cause change in responsiveness of the polymer to an aqueous alkaline solution or an aqueous acidic solution due to decomposition of side chain.
Further, as an example of laser-decomposable resin composition containing a compound which generates a base, a printing plate precursor capable of conducting laser engraving containing a developer generating a base and a color former is known (JP-A-2004-160898). However, the description of JP-A-2004-160898 does not suggest the combination of a polyurethane resin capable of being decomposed with a base and a base generator according to the invention. More specifically, JP-A-2004-160898 discloses the combination including a developer and a color former in order to form a dye having light absorption in a wavelength range of laser light after photo-curing and the combination does not satisfy the requirement of laser decomposability according to the invention. Further, when the decomposability of the resin is increased, a problem arises in that stability at the time of formation of thick layer decreases.